I posted this a few days ago but didn't have the OBD codes. Here's a description of the problem and the subsequently pulled OBD codes.

I have had a problem surface recently with my 94 (non-turbo) 940. Initially, it appeared a couple of weeks ago as a slight hesitation when accelerating somewhat agressively from a stop. Felt like the engine missed a couple of times. A gradual acceleration never caused the problem. Once up to 20 mph or so, hard accelerating never caused any hesitation. Thinking it might be a fuel supply problem, I replaced the fuel filter. Now, on occasion, the hesitation is more severe on acceleration - to the point that the car in this condition is undrivable - and seems to be associated with the engine reaching normal operating temperature. In this condition, it feels like the car is missing on half the cylinders. But at higher speeds there are no problems whatsoever. I also noticed that with each hesitation, the "service engine" light would illuminate briefly.

I pulled the codes. I assume this is a Motronics 1.8 since I got a code from Bank A, Socket #6. The code was 2-1-4. This is described in the OBD code document as
Fault condition: Ignition system RPM signal missing sporadically
Causes of Fault: Wiring fault or RPM sensor

Any suggestions on the best place to look given this code?????

I also got code 1-2-2 from Bank B, socket #2, associated with the cruise control. I don't know if this would have a bearing on the problem but may point to the RPM sensor - perhaps?

Thanks in advance for any help for this Volvo newbie.

Ron